This invention relates to a method and apparatus for subdividing a heated metal workpiece to form a number of billets each having a predetermined length which is selected to meet the requirements for operation of an extrusion press or other metalworking apparatus.
It is common practice to load a heated metal billet comprised of, for example, aluminum in a container of an extrusion press. At one end of the container there is a die through which material of the billet is forced by an extrusion stem that is advanced from the other end of the container by a ram. A dummy block may be situated between the billet and the stem. Billet material is extruded through the die until a small discard length of billet material remains in the billet container. By this type of extrusion operation, the stem or dummy block, if used, will not be brought into contact with the die; thereby avoiding possible damage to the die. The amount of billet discard material can be controlled by stopping the advancement of the press ram so that a preselected length of billet discard material remains in the billet container. However, extrusions having the same lengths cannot always be produced from billets having the same length. This is because the volume of billet material may change from time-to-time due to changes to the diameter of the billet. Also, wear of the extrusion die increases the required volume of billet material which is necessary to repeatedly produce extrusions having the same predetermined lengths. To compensate for wear of the die, billets having slightly increasing volumes of material must be supplied over an extended period of operation by the extrusion press. A conventional procedure for supplying billets to an extrusion press included supplying a succession of logs, i.e., workpieces, in an end-to-end relationship to a furnace wherein the log material is heated to a temperature for a subsequent extrusion process.
A heated log is pushed or driven out of the furnace through a log shear, until the log is engaged by a mechanical stop which has been adjustably positioned at a predetermined location to produce a desired billet length. Billets are cut from the log, and each billet length is subtracted from a premeasured log length so that an approximate remaining length of the log can be determined to accurately produce the final billet from the log. Elongation factors are used to estimate the heated log length based on the premeasured length to maximize the use of the entire log. However, hot and cold areas in the furnace affect the actual length which contributes to the difficulties encountered to an accurate remaining log length.
The present invention provides a method and apparatus for supplying billets having a predetermined length for use as workpieces in an extrusion press in which the lengths of billets can be accurately controlled by operation of a shear used to subdivide a log into the billets. The present invention also reduces waste of log material resulting from the shearing operation by maximizing the use of log end portions which may be too short to form a single billet but can be utilized to form one or more billets comprised of two log pieces.
In West German patent publication No. 32 15 798, there is disclosed a system and apparatus to control shearing of a heated metal log into billets through the use of a mechanical device arranged to detect the gap between the ends of two successively-arranged logs at the entry side of a shear. A mechanically-adjustable stop at the discharge side of the shear is connected by a push-pull cable to a carrier of an optical detector at the entry side of the shear. The stop can be moved between minimum and maximum billet lengths from the parting line between the shear knives whereby the push-pull cable moves the optical detector back and forth relative to the shear knife-parting line from a center position corresponding to one desired billet length. When the length of a log end portion extending between the shear and the detector is greater than a desired billet length, a short scrap end piece is cut. This procedure is wasteful of log material and necessitates the disposal of a very short log section which is likely to jam or otherwise cause malfunctioning of the billet-handling equipment at the discharge side of the shear.